We’ve seen the commercials featuring impossibly beautiful models, wolfing down massive cheeseburgers while grease drips onto their teeny bikinis. But in addition to being downright irritating to real-world women who feel like they gain five pounds merely driving past a fast-food restaurant, the image of a woman with a model physique making poor dietary choices can actually have pretty harmful effects on the general public. As it turns out, looks can be deceiving, and that seemingly fit woman may not be so healthy after all.

The tale of two fats

Most people are unconcerned about the type of fat they carry as long as they can fit into their skinny jeans. But there’s actually quite a bit of room for concern – especially as it relates to the type of fat that is stored.

Subcutaneous fat lies just below the skin, and though it can be aesthetically unappealing (cellulite, anyone?), it’s actually pretty harmless. Visceral fat, on the other hand, is deeper and surrounds the organs to act as a layer of protection, says Kusha Karvandi, a personal trainer and founder of the fitness app Exerscribe. It is this fat that can lead to major health issues like cardiovascular disease, stroke and diabetes. And, surprisingly, even thin people can carry unhealthy levels of visceral fat.

“A thin person can still be medically fat based on visceral internal body fat storage and blood lipid profiles blood fat,” Karvandi explains. “This is common in someone who may not overeat and has a fast metabolism, but chooses to be more sedentary and eats processed foods. When we eat processed foods, not only do we increase subcutaneous body fat, but we primarily gain visceral fat.”

Lies of the scale

We’ve heard for years that muscle weighs more than fat, so a very fit person with lots of lean muscle mass may actually be heavier than a thinner counterpart. And that’s exactly why you shouldn’t rely on your bathroom scale as your fitness barometer.

“Body fat is based on a ratio of total body weight, including lean body mass – muscles and organs – bones and fat,” says Lisa Reed, MS, founder of Lisa Reed Fitness. “So lower body weight does not directly translate into lower body fat. If you are sedentary and/or have restricted calorie diets there is a possibility of having body fat levels in the overweight and even obese levels [even if you don’t look like it].”

Diets that restrict certain (healthy) food groups like complex carbohydrates or protein, or that are too low in caloric intake to supply the fuel necessary for daily activities are of particular concern, Reed adds. These diets may lead to some weight loss, but not necessarily in the form of unhealthy fat, and they can also cause broken bones, hair loss, decreased energy levels and a host of other issues.

Fat and fit?

It is for this reason that Reed recommends body composition testing to determine true fat percentage and health, as opposed to just the scale. This testing will determine how much lean body mass a person has, as well as any other risk factors. “Some individuals believe that living an active lifestyle means they can eat whatever they want, which can negate some of the positive changes from exercising,” says Reed. “One must strength train to build muscle [while consuming] the right nutrients for her lifestyle and activity level to negate skinny fat consequences. The scale may be higher, as muscle weighs more than fat, but you burn more calories at rest, and in turn have a leaner body, a strong immune system and an abundant amount of energy.”

Indeed, more and more experts are noting that it is possible for people to carry more weight but still be fit based on overall health and fitness levels. In fact, Stan Reents, an ACSM-Certified Health Fitness Specialist and President/CEO of AthleteInMe.com believes that a person’s overall fitness level is the most important marker of health.

“Just in the past several years, researchers such as Dr. Steven Blair at the University of South Carolina have published reports showing that, if you are aerobically fit, this will offset the health risks of a few extra pounds,” he says. “Historically, a BMI value of up to 24.9 was considered acceptable, while a BMI value of 25-29.9 was considered overweight. This new research shows that health risks do NOT increase at BMI values of 25-26 if a person is aerobically fit. So, while the medical profession is monitoring traditional risk factors such as LDL-cholesterol levels and body weight, what we really should be monitoring is aerobic fitness level.”

When it comes to looking fit and actually being fit, the solution is tried and true: Karvandi recommends incorporating fat-soluble vitamins, enzymes and minerals into a healthy diet to begin to break down fatty acids in the liver (which serves as the primary processing factory for fat) while Reents and Reed suggest a comprehensive exercise program that includes both cardiovascular training and strength work.

It may not be as sexy as a supermodel clutching a double patty melt, but the end result certainly is.